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Abstract:

Employing a compact molded from powder of metal or the like as an
electrode 11, generating pulsed discharges between the electrode 11 and a
treating portion Wa of work W in working oil L as a mixture with powder
of semiconductor or conductor mixed therein, using discharge energy
thereof for locally fusing surface regions of the treating portion Wa of
work W, showering molten pieces of electrode material or reactants of the
electrode material onto the treating portion Wa of work W, forming a
covering film C on the treating portion Wa of work W.

Claims:

1. A coating block comprising a sintered compact comprising a powder of
ZrO2 mixed with at least one electrode material selected from the
group consisting of a powder of a metal, a powder of a metal compound, a
powder of a ceramic, and a powder of a nonconductive particle.

2. The coating block of claim 1, wherein a content of the ZrO2
powder is from 3% to 15% by weight to the electrode material.

3. The coating block of claim 2, wherein the content of the ZrO2
powder is 10% by weight to the electrode material.

4. The coating block of claim 1, wherein the electrode material is a
powder of a metal.

5. The coating block of claim 1, wherein the electrode material is a
powder of a metal compound.

6. The coating block of claim 1, wherein the electrode material is a
powder of a ceramic.

7. The coating block of claim 1, wherein the electrode material is a
powder of a nonconductive particle.

8. The coating block of claim 1, wherein the compact comprises a powder
of a chrome-containing cobalt alloy.

9. The coating block of claim 1, wherein a powder particle size of the
ZrO2 powder is from 5 to 10 μm.

10. The coating block of claim 1, wherein the sintered compact is a
sintered green pellet.

11. The coating block of claim 1, wherein the coating block is capable of
generating a discharge energy between the coating block and a treating
portion of work in a working oil.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a discharge surface treatment
method of forming a covering film on a treating portion of work using
discharge energy, and a coating block for discharge surface treatments.

BACKGROUND ART

[0002] There have been developments of various techniques for surface
treatment methods of forming a covering film on a treating portion of
work such as an engine component, involving recent active developments,
in particular, of discharge surface treatment methods using discharge
energy (Japanese Patent Application Laying-Open Publication Nos. 8-300227
and 2005-213554).

[0003] These discharge surface treatment methods included using a
compression-molded compact (a coating block) of powder of metal or the
like as an electrode, generating pulsed discharges between the electrode
and a treating portion of work in working oil. This involved making use
of attendant discharge energy, causing molten pieces of an electrode
material or reactants of the electrode material to be showered onto the
treating portion of work, affording to form a covering film onto the
treating portion of work.

SUMMARY OF THE INVENTION

[0004] There was a certain amount of pieces of electrode material or the
like showered onto the treating portion of work, of which about half
could fix (adhere) to the treating portion of work, forming a covering
film thereon, while the rest was unable to fix to the treating portion of
work, failing to provide a sufficient enhanced fixation ratio (film
forming rate) of electrode material or the like. Therefore, the yield of
electrode material was degraded, resulting in a high treatment cost of
discharge surface treatment, as a problem.

[0005] Further, to prevent concentrated discharges from being continued in
discharge surface treatment, upon occurrences of discharge concentration
the discharge was paused from time to time. In such the discharge surface
treatment, time intervals between discharges were extended, resulting in
an elongated treating time, with an insufficient enhanced productivity,
as a problem.

[0006] It is an object of the present invention to provide a new discharge
surface treatment method affording to solve the problems described.

[0007] To this end, according to a first aspect of the present invention
there is a discharge surface treatment method of forming a covering film
on a treating portion of work using discharge energy, the discharge
surface treatment method comprising: preparing an electrode as a compact
molded from one of a powder of metal, a powder of metal compound, a
powder of ceramics, and a mixed powder of at least two of them;
generating pulsed discharges between the electrode and a treating portion
of work in a volume of working oil prepared as a mixture with one of a
powder of semiconductor, a powder of conductor, a powder of nonconductive
particles; and a mixed powder of at least two of them, and using
discharge energy thereof for locally fusing surface regions of the
treating portion of work, showering molten pieces of a material of the
electrode or a reactant of the electrode material onto the treating
portion of work, forming a covering film on the treating portion of work.

[0008] According to a second aspect of the present invention there is a
coating block for discharge surface treatments of forming a covering film
on a treating portion of work using discharge energy, the coating block
for discharge surface treatments comprising a sintered compact of one of
electrode materials being a powder of metal, a powder of metal compound,
a powder of ceramics, and a mixed powder of at least two of them, the one
electrode material being combined with powder of a semiconductor ceramics
mixed therein.

BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a schematic illustration of a discharge surface treatment
system employed in a discharge surface treatment method according to a
first embodiment of the present invention.

[0010] FIG. 2 is a set of illustrations describing the discharge surface
treatment method according to the first embodiment of the present
invention.

[0011] FIG. 3 is a set of photographs showing a result of comparison of an
example of the discharge surface treatment method according to the first
embodiment of the present invention.

[0012] FIG. 4 is a set of graphs plotting results of comparison of other
examples of the discharge surface treatment method according to the first
embodiment of the present invention.

[0013] FIG. 5 is a schematic illustration of a discharge surface treatment
system employed in a discharge surface treatment method according to a
second embodiment of the present invention.

[0014] FIG. 6 is a set of illustrations describing the discharge surface
treatment method according to the second embodiment of the present
invention.

[0015] FIG. 7 is a graph plotting results of experiments on an example of
the discharge surface treatment method according to the first embodiment
of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

[0016] There will be described a first embodiment of the present invention
with reference to FIG. 1.

[0017] FIG. 1 illustrates a discharge surface treatment system 1 employed
in a discharge surface treatment method according to the first
embodiment, that includes a bed 3, and a table 5 mounted on the bed 3. On
the table 5 there is placed an oil tank 7 with a volume of electrically
insulating working oil L stored therein, having a work jig 9 put in the
oil tank 7, the work jig 9 being configured to set thereon a work W such
as an engine component.

[0018] Above the tale 5 there is an electrode 11 held by an electrode
holder 13 set in position. The electrode holder 13 is adapted to move
relative to the table 5 by combination of an X-axis servo motor
(non-depicted) drivable for displacements in the X-axis direction, a
Y-axis servo motor (non-depicted) drivable for displacements in the
Y-axis direction, and a Z-axis servo motor (non-depicted) drivable for
displacements in the Z-axis direction.

[0019] The electrode holder 13 as well as the work jig 9 is electrically
connected with a discharge power supply 15. The discharge power supply 15
may be a known discharge power supply such as that disclosed in Japanese
Patent Application Laying-Open Publication No. 2005-213554, and
configured with capacitors, switching elements, resistor elements, and
the like.

[0020] The electrode 11 is comprised of a compact (a coating block) as a
compression mold of powder of a chrome-containing cobalt alloy. It is
noted that the electrode 11 is not limited to a compact as a compression
mold of powder of a chrome-containing cobalt alloy, and may be a compact
molded from one of a powder of a metal or metals, a powder of a metal
compound or metal compounds (with an alloy or alloys inclusive), a powder
of ceramics, and a mixed powder of at least two of those powders.

[0021] Description is now made of the discharge surface treatment method
according to the first embodiment, with reference to FIG. 2.

[0022] The discharge surface treatment method according to the first
embodiment is based on a new knowledge such that in a state of working
oil L having mixed particles P of powder of semiconductor or conductor
such as Si or TiC for instance, there may be generation of pulsed
discharges between an electrode 11 as a compression mold of powder of a
chrome-containing cobalt alloy and a portion Wa of work W to be treated,
to have dispersed discharges during discharge surface treatment, allowing
for a sufficient enhanced fixation ratio (film forming rate), such as
that of electrode material, to the treating portion Wa of work W. This
may be thought due to particles P of powder of semiconductor or conductor
mixed in working oil L, causing discharges to be dispersed, decreasing
local treatment temperatures, suppressing evaporation of electrode
material.

[0023] For discharge surface treatment to a portion Wa of work W to be
treated, first there comes setting the work W to the jig 9, followed by
driving the X-axis servo motor and/or the Y-axis servo motor for moving
the electrode holder 13 together with the electrode 11 to displace in the
X-axis direction and/or the Y-axis direction relative to the table 5,
thereby placing the electrode 11 in preset position opposite to the
portion Wa of work W to be treated. This is followed by driving the
Z-axis servo motor for moving the electrode holder 13 together with the
electrode 11 to reciprocally displace in the Z-axis direction, while
operating the discharge power supply 15 to have pulsed discharges
generated, as illustrated in FIG. 2(a), between the electrode 11 and the
treating portion Wa of wok W in working oil L in a state having particles
P of semiconductor or conductor powder mixed therein. This involves
attendant discharge energies locally fusing surface regions of the
treating portion Wa of wok W, while showering molten pieces of electrode
material or reactants of the electrode material onto the treating portion
of wok W, affording as illustrated in FIG. 2(b) to form a covering film C
on the treating portion Wa of wok W.

[0024] Those particles P of powder of semiconductor or conductor added to
working oil L have their sizes within a range of 0.3 to 2.5 μm. For
the particles P of semiconductor or conductor powder, there is a lower
limit of size set to 0.3 μm, because of a concern to appear if under
0.3 μm, for possible reduction of a fixation ratio of electrode
material or the like to the treating portion Wa of wok W. On the other
hand, for the particles P of semiconductor or conductor powder, there is
an upper limit of size set to 2.5 μm, because of a concern to appear
if over 2.5 μm, for possible unstable discharges between the electrode
11 and the treating portion Wa of wok W.

[0025] For powder of Si used as powder P of semiconductor or conductor,
the amount of Si powder mixed in working oil L is set within a range of
0.5 to 30 g/l, and for powder of TiC used as powder P of semiconductor or
conductor, the amount of TiC powder mixed in working oil L is set within
a range of 1 to 100 g/l.

[0026] It is noted that powders used as additives in working oil L may
involve those of elements or alloys constituting residues or major
components of the electrode 11, encompassing oxides, carbides, nitrides,
and borides, as well as particles or short fibers made of carbon. For
uniform generation of discharges, about the electrode 11 there may be
dispersed non-conductive particles or semi-conductive particles to be
hardly reactive with electrode material in view of easy separation. The
dispersion of non-conductive particles is considered to be effective to
inhibit concentration of discharges, not for dispersion of discharges.

[0027] Description is now made of some examples of the discharge surface
treatment method according to the first embodiment, with reference to
FIGS. 3 and 4.

Embodiment Example 1

[0028] First, there was made a set of experiments for comparison to
examine an electrode consumption rate and a treatment time required to
form a covering film with a prescribed thickness in application of the
discharge surface treatment method according to the first embodiment. As
an embodiment example 1 using an electrode comprised of a compression
molded compact of chrome-containing cobalt alloy powder, there was a
covering film formed 0.30 mm thick in working oil with powder of Si mixed
therein (mixed amount of Si powder 1 g/l). Further, as a comparative
example 1 using an electrode comprised of a compression molded compact of
chrome-containing cobalt alloy powder, there was a covering film formed
0.30 mm thick in working oil with no powder of semiconductor or conductor
mixed therein. The embodiment example 1 and the comparative example 1 had
their treatment times of discharge surface treatment and consumption
rates in Z-axis direction of electrode (as feed amounts in Z-axis
direction), as shown in the Table 1 below.

[0029] As is apparent from comparison in between, relative to the
comparative example 1 the embodiment example 1 had more dispersed
discharges during discharge surface treatment, with discharge pulse pause
times shortened from 64 μs to 16 μs, allowing for a reduced
treating time of discharge surface treatment, as well as for a sufficient
enhanced fixation ratio of electrode material or the like to a treating
portion of work, with a reduced consumption rate in Z-axis direction of
electrode.

Embodiment Example 2

[0030] Next, there was made a set of experiments for comparison to
demonstrate a covering film formed with a uniform surface at a treating
portion of work by application of the discharge surface treatment method
according to the first embodiment. FIG. 3(a) shows, in a photograph, a
section of a covering film (as an embodiment 2) formed, by a discharge
surface treatment using a compression molded compact of chrome-containing
cobalt alloy powder as an electrode 11, in working oil L with ZrO2
particles added thereto, on a surface region (as a treating portion Wa)
of a substrate (work W) made of an aluminum alloy. Those ZrO2
particles then added had a powder particle size of 1.5 μm, the amount
added being 5 g/l. Working oil L was set to a flow rate of 300 cc/min. On
the other hand, FIG. 3(b) shows, in a photograph, a section of a covering
film (as a comparative example 2) formed, by a discharge surface
treatment using a compression molded compact of chrome-containing cobalt
alloy powder as an electrode 11, in working oil L free of additives, on a
surface region (as a treating portion Wa) of a substrate (work W) made of
an aluminum alloy. As is apparent from comparison in between, relative to
the comparative example 2 the embodiment example 2 had a covering film
surface formed more uniform in shape. Further, relative to the
comparative example 2 the embodiment example 2 had a densified structure
with less defects in the covering film. It can thus be found that using
the surface treatment method according to this embodiment enables a
covering film to be formed on a treating portion of work with an enhanced
uniformity over conventional surface treatment methods. This affords to
provide a covering film with enhanced film strength, as well.

Embodiment Example 3

[0031] In addition (as an embodiment example 3) there was made a set of
experiments for comparison to examine details of density and peel
strength of a covering film formed on a treating portion of work, using
the discharge surface treatment method according to the first embodiment.
FIG. 4(a) plots filling fractions of covering films each formed, by a
discharge surface treatment using a compression molded compact of
chrome-containing cobalt alloy powder as an electrode 11, in working oil
L with ZrO2 particles added thereto, on a surface region (as a
treating portion Wa) of a substrate (work W) made of an aluminum alloy.
FIG. 4(b) plots peel strengths of covering films each formed, by a
discharge surface treatment using a compression molded compact of
chrome-containing cobalt alloy powder as an electrode 11, in working oil
L with ZrO2 particles added thereto, on a surface region (as a
treating portion Wa) of a substrate (work W) made of an aluminum alloy.
Those ZrO2 particles then added had a powder particle size of 1.5
μm, and working oil L was set to a flow rate of 300 cc/min, while the
amount of ZrO2 particles added to working oil L was varied. In FIG.
4(a) and FIG. 4(b) there are plotted measures at amounts of 0 g/l, 1 and
5 g/l of ZrO2 particles added to working oil L. FIG. 4(a) and FIG.
4(b) each indicate conditions 1, 2, and 3, which refer to discharge
conditions. The discharge surface treatment method according to this
embodiment includes generation of pulsed discharges. In the embodiment
example 3, there was performed intermittent generation of stepped pulses
having two sets of peak current values being a set of peak current values
for initial periods, and a set of peak current values for intermediate
and subsequent periods. For each of the initial periods under the
conditions 1, 2, and 3, the peak current value was set to a common 30 A.
For the intermediate and subsequent periods, their peak current values
were set to be 1 A, 2 A, and 4.5 A. Pulse width was set to 8 μs, and
pulse pause time, to 64 μs. The electrode 11 was spaced from the
treating portion Wa of work W at Z-directional distances depending on gap
voltages causing discharges, which was about 50 μm. As will be seen
from FIG. 4(a) and FIG. 4(b), both filling rate and peel strength of
covering film increased, as the amount of added ZrO2 particles
increased. Such tendencies were not greatly changed even with yet
increased addition amounts. Instead, with addition amounts of 20 g/l or
more, the discharging got unstable. The tendencies in FIG. 4(a) and FIG.
4(b) were little changed, for instance whether the material of work W was
an alloy containing Fe, Ni, and Co as principal components or an alloy
containing well heat-conductive Cu and Al as principal components.
However, the optimum discharge condition was slightly changed in
dependence on the heat conductivity of material of the work.

Second Embodiment

[0032] There will be described a second embodiment of the present
invention with reference to FIG. 5.

[0033] FIG. 5 illustrates a discharge surface treatment system 100
employed in a discharge surface treatment method according to the second
embodiment, that includes a bed 3, and a table 5 mounted on the bed 3. On
the table 5 there is placed an oil tank 7 with a volume of electrically
insulating working oil L stored therein, having a work jig 9 put in the
oil tank 7, the work jig 9 being configured to set thereon a work W such
as an engine component.

[0034] Above the tale 5 there is an electrode 110 held by an electrode
holder 13 set in position. The electrode holder 13 is adapted to move
relative to the table 5 by combination of an X-axis servo motor
(non-depicted) drivable for displacements in the X-axis direction, a
Y-axis servo motor (non-depicted) drivable for displacements in the
Y-axis direction, and a Z-axis servo motor (non-depicted) drivable for
displacements in the Z-axis direction.

[0035] The electrode holder 13 as well as the work jig 9 is electrically
connected with a discharge power supply 15. The discharge power supply 15
may be a known discharge power supply such as that disclosed in Japanese
Patent Application Laying-Open Publication No. 2005-213554, and
configured with capacitors, switching elements, resistor elements, and
the like.

[0036] The electrode 110 is comprised of a compact (a coating block) as a
compression mold of powder of a chrome-containing cobalt alloy. It is
noted that the electrode 110 is not limited to a compact as a compression
mold of powder of a chrome-containing cobalt alloy, and may be a compact
molded from one of a powder of a metal or metals, a powder of a metal
compound or metal compounds (with an alloy or alloys inclusive), a powder
of ceramics, and a mixed powder of at least two of those powders. In the
second embodiment, the electrode 110 has particles of powder Q of a
semiconductor ceramics mixed therein in advance. In other words,
according to the second embodiment, the electrode 110 is comprised of a
compact (a coating block) made up by sintering a green pellet that has
particles of the semiconductor ceramics premixed to one electrode
material out of a group including a powder of a metal or metals, a powder
of a metal compound or metal compounds, a powder of ceramics, and a mixed
powder of at least two of those powders. As the semiconductor ceramics
premixed, there may be cited ZrO2, or else, powder of conductive
material may be mixed.

[0037] Description is now made of the discharge surface treatment method
according to this embodiment, with reference to FIG. 6.

[0038] The discharge surface treatment method according to the second
embodiment is based on a new knowledge such that in working oil L there
may be generation of pulsed discharges between an electrode 110 as a
compression mold of powder of a chrome-containing cobalt alloy with a
prescribed amount of powder Q of ZnO2 premixed thereto and a portion
Wa of work W to be treated, to have dispersed discharges during discharge
surface treatment, allowing for a sufficient enhanced fixation ratio
(film forming rate) of electrode material or the like to the treating
portion Wa of work W. This may be thought due to powder particles Q of
ZnO2 fused together with an electrode material or reactants of the
electrode material and dispersed in working oil L, causing discharges to
be dispersed, decreasing local treatment temperatures, suppressing
evaporation of electrode material.

[0040] For discharge surface treatment to a portion Wa of work W to be
treated, first there comes setting the work W to the jig 9, followed by
driving the X-axis servo motor and/or the Y-axis servo motor for moving
the electrode holder 13 together with the electrode 110 to displace in
the X-axis direction and/or the Y-axis direction relative to the table 5,
thereby placing the electrode 110 in preset position opposite to the
portion Wa of work W to be treated. This is followed by driving the
Z-axis servo motor for moving the electrode holder 13 together with the
electrode 110 to reciprocally displace in the Z-axis direction, while
operating the discharge power supply 15 to have pulsed discharges
generated, as illustrated in FIG. 6(a), between the electrode 110 and the
treating portion Wa of wok W in working oil L. This involves attendant
discharge energies locally fusing surface regions of the treating portion
Wa of wok W, while showering molten pieces of electrode material or
reactants of the electrode material onto the treating portion of wok W,
affording as illustrated in FIG. 6(b) to form a covering film C on the
treating portion Wa of wok W.

[0041] The discharge surface treatment method according to the second
embodiment permits the film forming rate (as the covering film generation
rate) to be enhanced two to three folds in comparison with discharge
surface treatments using an electrode without premixed powder Q of
semiconductor ceramics in electrode 110. This is accompanied by a
consumption rate of electrode 110 proportional to the generation rate of
covering film. Also, there is enhancement of a fixation ratio of
electrode material to the treating portion Wa of work W.

[0042] Description is now made of an example of the discharge surface
treatment method according to the second embodiment, with reference to
FIG. 7.

Embodiment Example

[0043] FIG. 7 plots in a graph a relationship the treating rate of film
formation (as the film forming rate) had to addition amounts of ZnO2
powder Q premixed in electrodes 110 having a chrome-containing cobalt
alloy powder as an electrode material thereof. As used herein, the film
forming rate means a height of film formed per one minute (as a cladding
rate) at a treating portion Wa of work W. Added ZnO2 powder Q had
particle sizes of 5 to 10 μm. Specific values of plot data in FIG. 7
were as shown in Table 2 below.

[0044] As will be seen from Table 2, it is found that using an electrode
110 with an addition amount of 10% by weight of ZnO2 powder Q in the
discharge surface treatment method according to the second embodiment
does permit the treating rate of film formation to be enhanced about 3.5
folds or near in comparison with a discharge surface treatment using an
electrode without premixed powder Q of ZnO2 in electrode 110
(corresponding to an addition amount of 0 wt % of ZnO2 powder Q in
Table 2). Also from FIG. 7, it is found that the treating rate has a
maximum value with an addition amount of ZnO2 powder Q in a vicinity
of 10 wt %. More specifically, there is seen such a tendency that the
treating rate of film formation rises at an addition amount of ZnO2
powder Q near 3 wt %, getting maximum near 10 wt %, and afterward,
gradually decreases to converge on a steady value to be held past 15 wt %
or near.

[0045] The present invention is not limited to the embodiments described.
For instance, the first embodiment and the second embodiment may be
combined to provide another embodiment. That is, there may be combined
use of a volume of working oil prepared as a mixture with one of a powder
of semiconductor, a powder of conductor, a powder of nonconductive
particles, and a mixed powder of two or more of those powders, and a
compact (as a coating block) of an electrode material made of one of a
powder of metal, a powder of metal compound, a powder of ceramics, and a
mixed powder of two or more of these powders, having a powder of
semiconductor ceramics premixed thereto. Also, the scope of appended
claims is limited to the embodiments described.

INDUSTRIAL APPLICABILITY

[0046] According to the first embodiment of the present invention there is
generation of pulsed discharges between an electrode and a portion of
work to be treated in a volume of working oil prepared as a mixture with
one of a powder of semiconductor, a powder of conductor, a powder of
nonconductive particles, and a mixed powder of at least two of those
powders, thus having dispersed discharges during discharge surface
treatment, allowing for a sufficient enhanced fixation ratio of electrode
material or the like to the treating portion of work.

[0047] According to the second embodiment of the present invention there
is use of a compact (as a coating block) of an electrode material made of
one of a powder of metal, a powder of metal compound, a powder of
ceramics, and a mixed powder of at least two of those powders, having a
powder of semiconductor ceramics premixed thereto, as an electrode for
generating pulsed discharges between the electrode and a portion of work
to be treated, thus having dispersed discharges during discharge surface
treatment, allowing for a sufficient enhanced fixation ratio of electrode
material or the like to the treating portion of work.

[0048] According to the present invention, there is a system of discharges
dispersed in a field discharge surface treatment, constituting a
difficulty to cause concentrated discharges, affording to minimize time
intervals between discharges in discharge surface treatment, permitting
the treatment time to be shortened, allowing for well enhanced
productivity.

[0049] Further, the treating portion of work is afforded to have a
sufficient enhanced fixation ratio of electrode material or the like to
the treating portion of work, to increase the yield of electrode,
allowing for a reduced treatment cost in the discharge surface treatment.